One example of a gas turbine engine is a turbofan, gas turbine engine of the type used to propel aircraft. The turbofan engine has a primary flowpath for working medium gases which is annular in shape. The annular flowpath extends through a compression section, a combustion section, and a turbine section. The engine has a rotor assembly which extends axially through these sections of the engine. A stator assembly, which includes an engine case, extends axially through the engine outwardly of the rotor assembly to bound the working medium flowpath and to support the rotor assembly of the engine.
A secondary flowpath for working medium gases is annular in shape and extends axially rearward through the engine outwardly of the primary flowpath. The stator assembly includes a portion of the engine case which provides an inner boundary to the secondary flowpath and a portion of a fan duct which provides an outer boundary to the flowpath.
During engine operation, fuel is supplied to the combustion section where it is burned to produce energy. The energy is used to develop a propulsive thrust and to drive the rotor assembly about an axis of rotation. Hydraulic and lubricating fluids are supplied to other sections of the engine for hydraulic actuators and for lubricating moving components.
The fuel, hydraulic and lubricating systems may develop small, intermittent leaks which occur during engine operation. As a result, fluids may accumulate at very low rates at the bottom of the engine on the interior of the engine case. Because these fluids are flammable, it is desirable to drain the fluids via an opening in the engine case into the secondary flowpath. The large volume of rushing gases in the secondary flowpath sweeps away any small amount of fluid draining from the case during engine operation at a flammable fluid to air ratio which does not support combustion.
One disadvantage of a drain opening is that the opening provides a path for flames to the inside should a fire occur outside the engine or a path for flames to the outside should a fire occur on the inside of the engine. Accordingly, it is desirable to provide a device for draining fluids from the case that blocks flames from passing through the device from the inside of the case to the outside or from the outside to the inside.
One example of a device which might be used in other fields is shown in U.S. Pat. No. 1,960,259 entitled "Safety Device" which was issued to Wyman. In the Wyman construction, a plug threadably engages a case. The case has an axially extending inlet passage, an axially extending outlet passage, and an axially extending apparatus for blocking flames which extends from the inlet to the outlet passage. The apparatus includes a number of axially spaced disks. Each disk has a chordal segment cut away to provide an opening which axially faces the adjacent disks. This forms a tortuous path from the inlet to the outlet which is easily followed by the draining fluid while providing an effective device for blocking the passage of flames.
It is important in gas turbine engines to avoid using a drain assembly which intrudes into the secondary flowpath because the intrusion disrupts the flow in the secondary flowpath with a concomitant decrease in aerodynamic performance. In addition, it is important to minimize how far the device extends into the engine interior because of close clearances between the engine case and structures on the interior of the engine. The clearances are kept close to minimize the radial profile of the engine which decreases drag on the engine during operative conditions.
Accordingly, scientists and engineers working under the direction of Applicants, assignee are working to develop a drain assembly for an engine case, which has a low profile to fit in the clearance between the engine case and structure inwardly of the engine case, and which allows fluids to freely flow from the interior while providing a barrier to flames.